1. Field of the Invention
The present invention relates to an exposure apparatus and a device manufacturing method.
2. Description of the Related Art
An exposure apparatus is an apparatus that exposes a pattern of an original (reticle or the like) onto a photosensitive substrate (e.g., wafer where the surface thereof is coated with a resist layer) via a projection optical system in a lithography process of a manufacturing step for a semiconductor device or the like. There is also an immersion exposure apparatus that uses an immersion method as a technique to enhance the resolution of a pattern image that is projected onto a substrate. The immersion exposure apparatus is configured to fill an interval between the final lens of the projection optical system and the substrate with an immersion liquid and to project the pattern image onto the substrate. On the other hand, to improve productivity per unit time, the immersion exposure apparatus may also be provided with plural stages configured to retain a substrate. In the immersion exposure apparatus having only a single substrate stage, an exposure operations is not possible when replacing the substrate or when pre-measuring, and therefore results in a so-called “down time”. On the other hand, an immersion exposure apparatus provided with plural substrate stages (for example, two substrate stages) can expose a substrate on one substrate stage while replacing a substrate on the other substrate stage. This configuration allows the immersion exposure apparatus to start exposure of the next substrate on the other substrate stage immediately after completion of exposure of the substrate on the first substrate stage. That is to say, “down time” does not occur when the overall immersion exposure apparatus is considered, and productivity per unit time is enhanced by a configuration in which exposure of one of the substrates is constantly performed.
In this context, an immersion exposure apparatus having plural substrate stages firstly completes exposure of the substrate on one substrate stage, and then rapidly moves another substrate stage below the projection optical system and starts exposure of the next substrate with the result that immersion liquid is delivered between each substrate stage. For example, a method has also been proposed in which supply of immersion liquid is stopped when exposure of one substrate is completed, and supply of the immersion liquid is restarted when another substrate stage moves below the projection optical system. However, this method is not practical due to the fact that time is required to stabilize the state of the supplied immersion liquid after starting supply of the immersion liquid. In this context, a method has been proposed in which immersion liquid that is supplied is delivered without modification from the substrate stage that retains the exposed substrate to the substrate stage that retains the substrate that is the subject of the next exposure operation. Japanese Patent Application Laid-Open No. 2008-124219 discloses an immersion exposure apparatus that predetermines a delivery position of immersion liquid on each substrate stage. This immersion exposure apparatus includes a mirror that is provided on a side of each substrate stage and is used to measure the position of each substrate stage in real time during an exposure operation. The delivery position of immersion liquid in this case is taken to be the end of the substrate stage to thereby avoid hindrance to measurement using the mirror. On the other hand, Japanese Patent Application Laid-Open No. 2008-130745 discloses an immersion exposure apparatus that includes a plurality of delivery positions for immersion liquid on the substrate stage in order to reduce the delivery time.
However, the immersion exposure apparatus disclosed in Japanese Patent Application Laid-Open No. 2008-124219 requires that the path through the predetermined delivery position is always followed during delivery of immersion liquid, and therefore may result in wasted time during deliver depending on the position of the substrate stage when delivery is commenced. Furthermore, the immersion exposure apparatus disclosed in Japanese Patent Application Laid-Open No. 2008-130745 requires an increase in the operational area of the substrate stage in order to deliver immersion liquid. As a result, the size or cost of the apparatus may increase.